IP television or IPTV is the name given to a range of services which allow television to be delivered over an IP network. Due to the flexible nature of an IP network, IPTV will allow for a much more personalised service to users, e.g. video-on-demand, with information delivered to users over unicast IP streams. However, to order and control these user specific services, the user would normally be expected to use his or her remote control whilst sitting in front of a Set-Top-Box (STB)/TV. Currently the predominant way of controlling these unicast streams is to use the real time streaming protocol (RTSP). RTSP does not specify a transport protocol but may be used, for example, to establish and control real-time transport protocol (RTP) media streams. RTSP is in many ways similar to the HTTP protocol used to request and exchange information over the web, but is tailored for streaming media such as audio and video. RTSP allows a client to request particular media streams from a streaming server, and specifies commands such as PLAY and PAUSE. RTSP is well suited to the conventional set-top-box use case.
It is expected that users of mobile terminals such as mobile telephones will wish to avail themselves of IPTV services. Indeed, this is probably key to the business models of network operators currently installing high capacity cellular networks such as 3G networks. Within cellular networks, IPTV is a service which will likely be facilitated by the so-called IP Multimedia Subsystem (IMS). IMS is the technology defined by the Third Generation Partnership Project (3GPP) to provide IP Multimedia services over mobile communication networks (3GPP TS 22.228, TS 23.218, TS 23.228, TS 24.228, TS 24.229, TS 29.228, TS 29.229, TS 29.328 and TS 29.329), although the IMS architecture is such that its services can be accessed and controlled via other interfaces, for example the fixed access network. IMS makes use of the Session Initiation Protocol (SIP) to set up and control calls or sessions between client terminals, or client terminals and application servers. The Session Description Protocol (SDP), carried by SIP signaling, is used to describe and negotiate the media components of the session. Whilst SIP was created as a user-to-user protocol, IMS allows operators and service providers to control user access to services and to charge users accordingly.
It will be appreciated that IMS and RTSP have traditionally been considered as alternative approaches for the establishment and control of unicast streaming sessions. Whilst IMS provides a mechanism for controlling QoS and charging, as well as transcoder negotiation, RTSP supports trickplay and basic video-oriented commands.
A number of systems are currently on the market which allow a user to control a STB remotely over the Internet. These include LocationFreeTV™ from Sony Corporation and Slingbox™ from Sling Media. Both of these systems allow a user to instruct the delivery of media from the home STB to a client terminal (e.g. a STB or a television in a hotel room in which a user is staying).